PV calculator

What a homeowner wants to see
* Total up front costs
* Percentage of offset
* payback
* rebates

Notes
dsire.org is a site for federal rebates
consider the 4.5% increase in utility prices
the azimuth angle for south is 180 degrees
to determine the square footage of a system
 - avg sqft per panel is 18
 - avg watts per panel is 270
Need homeowners annual kwhs/year
- api call for avg cost per kwh by state
    http://api.eia.gov/series/?api_key=YOUR_API_KEY_HERE&series_id=ELEC.PRICE.#{state in 2 letter abbr.}-RES.A
    
Big thing is what is the payback???